A swash plate type capacity-variable compressor used in an air-conditioning system of an automobile or the like is provided with a rotary shaft that is rotated and driven by a rotation force of an engine, a swash plate connected to the rotary shaft with a variable inclination angle, a piston for compression that is connected to the swash plate and the like. This capacity-variable compressor controls the amount of refrigerant gas discharged while changing the stroke of the piston by changing the inclination angle of the swash plate.
The inclination angle of the swash plate can be continuously changed by adjusting a pressure balance acting on both faces of the piston through appropriate control of a pressure in a control chamber using a capacity control valve opening/closing-driven by an electro-magnetic force while using a suction pressure of a suction chamber into which a refrigerant gas is sucked, a discharge pressure of a discharge chamber from which the refrigerant gas pressurized by a piston is discharged, and a control chamber pressure of the control chamber (crank chamber) in which the swash plate is accommodated.
The capacity control valve includes a lead-in passage through which the discharge chamber and the control chamber are allowed to communicate with each other and through which a discharge fluid (refrigerant gas) is introduced into the control chamber, a first valve chamber formed in an enlarged shape at a place on the lead-in passage, a lead-out passage through which the suction chamber and the control chamber are allowed to communicate with each other and through which a fluid (e.g., refrigerant gas or blow by gas) is led out from the control chamber, a second valve chamber formed in an enlarged shape at a place on the lead-out passage, a valve body in which a first valve part that is disposed in the first valve chamber and that opens and closes the lead-in passage and a second valve part that is disposed in the second valve chamber and that opens and closes the lead-out passage are reciprocated together, and, at the same time, perform an open-close operation in mutually opposite directions (i.e., the second valve part is fully closed (or fully opened) when the first valve part is fully opened (or fully closed)), and a solenoid that operates the valve body, which is formed so that a discharge pressure acts on one side (first valve part side) of the valve body and a suction pressure acts on an opposite side (second valve part side) thereof, with an electro magnetic force so as to perform an open-close operation (see Patent Documents 1 and 2, for example).
Further, in this capacity control valve, a control-chamber pressure acts on the first valve part that receives a discharge pressure from an opposite side, and a control-chamber pressure acts on the second valve part that receives a suction pressure from an opposite side. With this structure, the influence of the control-chamber pressure on the valve body is counterbalanced, and only a differential pressure between the discharge pressure and the suction pressure is caused to act on the valve body so as to control the control-chamber pressure.
By the way, attention is paid to carbon dioxide (CO2) to be used as a refrigerant gas serving as the replacement of a fron gas. The carbon dioxide is about ten times as great as the existing refrigerant gas in the pressure area (i.e., in pressure fluctuation width) to be used, and a differential pressure acting on the valve body becomes great because of a structure in which the two passages (i.e., the lead-in passage through which a discharge pressure and a control-chamber pressure are allowed to communicate with each other and the lead-out passage through which a suction pressure and a control-chamber pressure are allowed to communicate with each other) are opened and closed. As a result, when the valve body controls a fluid flow (i.e., flow rate), a differential pressure between the discharge pressure and the control-chamber pressure becomes greater than a differential pressure between the suction pressure and the control-chamber pressure, and hence the fluid flow of the lead-out passage opened and closed by the second valve part is a tendency to become shorter than the fluid flow of the lead-in passage opened and closed by the first valve part.
Therefore, to eliminate this tendency, there is a need to make the passage area of the lead-out passage opened and closed by the second valve part (and the opening area of a valve seat) greater than the passage area (opening area) of the lead-in passage opened and closed by the first valve part. If the opening area (passage area) is increased, a differential pressure caused by the control-chamber pressure is increased. Therefore, to maintain the balance of a force exerted on the valve body, the driving force of the solenoid by which the valve body is driven is required to be increased, in other words, the solenoid is required to been enlarged. This brings about an increase in device size and an increase in cost.
Patent Document 1: Unexamined Japanese Patent Publication No. 2003-328936
Patent Document 2: Unexamined Japanese Patent Publication No. 2004-116407